BQ27541: proxy calculation for state of health

Lenio Cacula

Part Number: BQ27541

I realize the bq27541 does not have a state of health register available, but I think I can estimate how far the battery is from its end-of-life by comparing full available capacity with design capacity. Would you agree with that approach? Do you have other suggestions?

Thank you!

over 4 years ago

0 Andy Liu (BMS) over 4 years ago

TI__Guru 52115 points

Hi Lentio,

Yes if you are just looking for an easy estimate, based on the information bq27541 can offer. However, you require an accurate SOH. I would recommend using newer gauge devices which can provide SOH directly.

Andy

0 Lenio Cacula over 4 years ago in reply to Andy Liu (BMS)

TI__Genius 15890 points

Andy,

a new part is not an option at the moment. A follow up question from the customer is whether this method can also be used for identifying a defective battery; some field returns show swollen and blistered battery packs. The customer believes that the internal resistance of the battery could be used to correlate to those defective units. Do you have comments about that?

Thank you!

0 Kang Kang over 4 years ago in reply to Lenio Cacula

TI__Mastermind 24870 points

Hello Lenio,

You will want to use cycle count instead of SOH. It is not an SBS register, but it should get you the number of cycles, but not all cycles are created equal. SOH is a measure for a fixed lab test.

0 Lenio Cacula over 4 years ago in reply to Kang Kang

TI__Genius 15890 points

HI Kang Kang,

thanks for the reply, but I think those battery packs are failing prematurely - which is only a suspicion at this point. Having a parameter that could correlate to those early failures could prove or disprove the theory. Do you have any suggestions? Do you think abnormally elevated internal resistance could be that parameter?

Thank you!

0 Kang Kang over 4 years ago in reply to Lenio Cacula

TI__Mastermind 24870 points

Hello Lenio,

There are multiple ways to do this, but it really depends on your use case and your system.

If you have return data and see a correlation in the returned packs lifetime or gg files, then I would recommend looking at those specific parameters that look abnormal.

SOH is more of a general lab environment type of test, it does not necessarily relate to what you are after, which is preemptively determining if a battery needs to be replaced.

0 Lenio Cacula over 4 years ago in reply to Kang Kang

TI__Genius 15890 points

Kang Kang,

is there a way to extract the internal resistance calculated in the bq27541?

Thanks!

0 Kang Kang over 4 years ago in reply to Lenio Cacula

TI__Mastermind 24870 points

Hello Lenio,

For room temperature, it is the Ra tables. You can find the subclass IDs in the TRM.

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BQ27541: proxy calculation for state of health